Perforated screens are ubiquitous in architecture - in both external facades and interiors throughout the world. They can be used to provide and control both light and ventilation. External perforated screens are often used to provide daylight and solar shading. In hot climates perforated walls are regularly used to provide natural ventilation.

The picture below-left shows an example from the Leventis Art Gallery by FCBS and Max Fordham where an external perforated metal screen, in conjunction with glazing, is used to provide daylight and dappled shade. The second picture shows the DPS Kindergarten School by Khosla Associates where the whole façade acts as a screen, providing natural ventilation, light, solar shading and beautiful patterns cast from transmitted sunlight.

A moiré screen can be formed from 2 (or more) perforated panels in series; constructed from materials such as steel, aluminium or timber. As with any perforated material, light and air can pass through the holes, the extent being related to the density of perforation or pattern openness.

For thin screens (such as sheet metal) the light transmission is very nearly the same as the 'openness percentage' (the area of hole divided by the total face area). As part of our exhibition in the Process series at Scene gallery, a range of moiré pattern screens were created using perforated steel mesh on a light box. The openness of the patterns was calculated by processing digital photographs of the screens. Some results are illustrated below.

Moiré screens could be used in facades to provide and control natural ventilation. We have used computational fluid dynamics (CFD) to model and simulate the air flow properties though a set of moiré screens at different rotation angles. The model set up and results are illustrated below.

A useful feature of some moiré patterns is that very small movements can yield large changes in transmission. Think about perforated screens, two perfectly aligned, both with chess board patterns. When one screen is shifted sideways the width of one square, the whole panel, irrespective of the overall size changes form 50% open to 0% open. The square size could be 10mm and the overall panel size could be 10m. Other useful effects a can be created when one considers adding thickness or a profile to a moiré screen. When this is done the light transmission is no longer equal to the openness, it can vary a great deal depending on the design of the aperture and the angle of the incoming light.  An example of this in a hypothetical rotary moiré screen is illustrated below.

Given the right engineering, moiré screens could be utilised at any scale, from portholes to entire facades. The animation below shows how moiré screens used for daylight modulation might look when integrated into a glazed façade.

Rotary moiré screen to control daylight

The MAX:R+I work on Moiré screens was initiated by an invitation from Scene to produce work for their 'Process' series of events. Moiré Screens (as an exhibit) comprises a number of interactive lighting installations with supporting 2D works. It has been exhibited at the Depot, Clapton and again at the DreamSpace gallery, both in East London.  

One of our installations, Moiré Projector uses a triple LED light source to shine light through a rotary moiré screen composed of 2 layers of perforated sheet steel. In this case both layers use the same hole pattern of circles in a triangular layout. The resulting moirés are hexagon forms that change scale as the viewer rotates one screen by hand. The pattern forms on the wall beyond as a projection of light and shade. Due to the use of multiple light sources the resulting pattern is formed from three slightly overlapping layers creating a slightly distorted effect with a 3D relief quality.

Moiré Projector in use

A second installation, Moiré Bands, uses two layers of steel mesh in front of a wall-hung light box. The piece includes a handle that the viewer can use to both rotate and translate one of the mesh layers. In this case the two constituent layers have different patterns; one uses circular holes in a triangle pattern, while the other uses circles in a square pattern. The result is a set of moiré bands that undulate and twist under the control of the viewer.